The invention relates to the field of gas and petroleum refining industry, in particular to methods for hydrogen sulphide and/or mercaptans decomposition and recycling hydrogen sulphide and mercaptans (thiols) and can be used for producing hydrogen and sulfur from hydrogen sulphide as well as for purification of gas mixtures from hydrogen sulphide and mercaptans.
Hydrogen sulphide is the major byproduct in petroleum industry and hydrometallurgy. It is present in large quantities (up to 50%) in gas-condensate fields of natural gas. It is the major product of many mineral and organic substance decomposition. At the same time hydrogen sulphide is a strong toxic substance causing poisoning of living organisms. Yet hydrogen sulphide can be a feed stock for producing valuable chemical product—hydrogen.
Mercaptans are byproducts of mineral and organic substances decomposition. They are present as admixtures in gaseous products of petroleum refinery. They can be present in gas-condensate fields of natural gas. Mercaptans are toxic substances with highly objectionable odor. Therefore off gases of industrial plants should be thoroughly cleaned of mercaptans. At the same time mercaptans are widely used as odorants of household gases to detect gas escape. Mercaptan presence in hydrocarbon gases leads to deactivation of catalysts used for conversion of these gases into valuable products. For that reason said gases should be purified from mercaptans.
Hydrogen sulphide is directly thermally decomposed into hydrogen and sulfur according to reaction:H2SH2+S−Q   (1)
It is a strongly endothermic process and can have visible rate only at high temperatures. A method for thermal decomposition of hydrogen sulphide for obtaining hydrogen and sulfur is known. The method comprises passing hydrogen sulphide containing gas through a reaction zone at a temperature in the range from 850 to 1600° C. where decomposition of H2S results in obtaining hydrogen and sulfur, and consequent cooling of said gas to a temperature of 110-150° C. for condensing obtained sulfur (see U.S. Pat. No. 4,302,434, C01B 17/04, 24 Nov. 1981).
The known method has a few disadvantages: high temperature required for achieving high degree of hydrogen sulphide decomposition; high energy consumption for performing the reaction and compensating possible heat loss; potential decrease in decomposition level due to reverse interaction of hydrogen and sulfur on cooling; unsuitability of the method for treating gases containing hydrocarbons and other admixtures that can be pyrolyzed at high temperature; low effectiveness of the process when the concentration of hydrogen sulphide in the hydrogen sulphide containing feed decreases; requirements to use special expensive materials of high thermal resistance to form a high temperature reaction zone. What is more performing the hydrogen sulphide decomposition reaction at high temperature results in formation of gaseous sulfur consisting of high energy molecules S2. It has adverse influence on the general thermodynamics of the process since it is known that producing products with less energy in condensed state (liquid or solid) is favorable for shifting reaction balance to formation of reaction products.
However it is possible to use catalysts for directing reaction (1) so that it can be performed at lower temperature.
Such possibility is disclosed in an invention (RU 2216506, C10B 17/04, 20 Nov. 2003) where hydrogen sulphide containing gas is passed through the layer of a solid catalytic material capable to decompose hydrogen sulphide according to reaction (1) at a temperature lower that 200° C., and regeneration is performed by supplying regenerating gas without hydrogen sulphide at a temperature at most 350° C. This method is the closest prior art.
A disadvantage of the known method is rather frequent regeneration of the solid material capable of decomposing hydrogen sulphide since obtained sulfur according to reaction (1) accumulates on its surface and block centers of hydrogen sulphide activation.
It is an object of the invention to provide a more effective method of hydrogen sulphide and/or mercaptans containing gases decomposition without frequent regeneration of the solid catalytic material.